Japanese Patent Application publication No. 2012-206840 discloses an image-forming apparatus provided with a sheet supplying tray below which an additional sheet-supplying device is attachable as an extension unit. The disclosed device is provided with a sheet supplying path for conveying a sheet accommodated in the sheet supplying tray, and a sheet conveying path provided at the sheet supplying tray. The sheet supplying path is open downward to provide communication with the sheet conveying path. A sheet accommodated in the additional sheet-supplying device can be supplied to the sheet supplying path through the sheet conveying path.